Decreased expression and increased oxidation of plasma haptoglobin in Alzheimer disease: Insights from redox proteomics

Alzheimer disease (AD) is one of the most disabling disorders of the elderly and the number of people worldwide facing dementia is expected to dramatically increase in the near future. Thus, one of the major concerns of modern society is to identify putative biomarkers that serve as a valuable early diagnostic tool to identify a subset of patients with increased risk to develop AD. An ideal biomarker should be present in blood before dementia is clinically confirmed, have high sensitivity and specificity, and be reproducible. Proteomics platforms offer a powerful strategy to reach these goals and recently have been demonstrated to be promising approaches. However, the high variability of technologies and studied populations has led to contrasting results. To increase specificity, we analyzed both protein expression profiles and oxidative modifications (carbonylation) of plasma proteins in mild cognitive impairment (MCI) and AD subjects compared with age-matched controls. Most of the proteins found to have differential levels in MCI and AD confirmed results already obtained in other cohort studies. Interestingly, we applied for the first time in MCI a redox proteomics approach to specifically identify oxidized proteins. Among them, haptoglobin, one of the most abundantly secreted glycoproteins with chaperone function, was found to be either increasingly downregulated or increasingly oxidized in AD and MCI compared with controls. We also demonstrated that in vitro oxidation of haptoglobin affects the formation of amyloid-β fibrils, thus suggesting that oxidized haptoglobin is not able to act as an extracellular chaperone to prevent or slow formation of amyloid-β aggregates. Another chaperone protein, α2-macroglobulin, was found to be selectively oxidized in AD patients compared with controls. Our findings suggest that alterations in proteins acting as extracellular chaperones may contribute to exacerbating amyloid-β toxicity in the peripheral system and may be considered a putative marker of disease progression.

Role of human CYP1A1 and NAT2 in 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine-induced mutagenicity and DNA adducts

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is carcinogenic in multiple organs and numerous species. Bioactivation of PhIP is initiated by PhIP N(2)-hydroxylation catalysed by cytochrome P450s. Following N-hydroxylation, O-acetylation catalysed by N-acetyltransferase 2 (NAT2) is considered a further possible activation pathway. Genetic polymorphisms in NAT2 may modify cancer risk following exposure. Nucleotide excision repair-deficient Chinese hamster ovary (CHO) cells stably transfected with human cytochrome P4501A1 (CYP1A1) and a single copy of either NAT2*4 (rapid acetylator) or NAT2*5B (slow acetylator) alleles were used to test the effect of CYP1A1 and NAT2 polymorphism on PhIP genotoxicity. Cells transfected with NAT2*4 had significantly higher levels of N-hydroxy-PhIP O-acetyltransferase (p = 0.0150) activity than cells transfected with NAT2*5B. Following PhIP treatment, CHO cell lines transfected with CYP1A1, CYP1A1/NAT2*4 and CYP1A1/NAT2*5B each showed concentration-dependent cytotoxicity and hypoxanthine phosphoribosyl transferase (hprt) mutagenesis not observed in untransfected CHO cells. dG-C8-PhIP was the primary DNA adduct formed and levels were dose dependent in transfected CHO cells in the order: CYP1A1 < CYP1A1 and NAT2*5B < CYP1A1 and NAT2*4, although levels did not differ significantly (p > 0.05) following one-way analysis of variance. These results strongly support activation of PhIP by CYP1A1 with little effect of human NAT2 genetic polymorphism on mutagenesis and DNA damage.

Alterations in brain antioxidant enzymes and redox proteomic identification of oxidized brain proteins induced by the anti-cancer drug adriamycin: implications for oxidative stress-mediated chemobrain

Adriamycin (ADR) is a chemotherapeutic for the treatment of solid tumors. This quinone-containing anthracycline is well known to produce large amounts of reactive oxygen species (ROS) in vivo. A common complaint of patients undergoing long-term treatment with ADR is somnolence, often referred to as "chemobrain." While ADR itself does not cross the blood brain barrier (BBB), we recently showed that ADR administration causes a peripheral increase in tumor necrosis factor alpha (TNF-alpha), which migrates across the BBB and leads to inflammation and oxidative stress in brain, most likely contributing to the observed decline in cognition. In the current study, we measured levels of the antioxidant glutathione (GSH) in brains of mice injected intraparitoneally (i.p.) with ADR, as well as the levels and activities of several enzymes involved in brain GSH metabolism. We observed significantly decreased GSH levels, as well as altered GSH/GSSG ratio in brains of ADR treated mice relative to saline-treated controls. Also observed in brains of ADR treated mice were increased levels of glutathione peroxidase (GPx), glutathione-S-transferase (GST), and glutathione reductase (GR). We also observed increased activity of GPx, but a significant reduction in GST and GR activity in mice brain, 72 h post i.p. injection of ADR (20 mg/kg body weight). Furthermore, we used redox proteomics to identify specific proteins that are oxidized and/or have differential levels in mice brains as a result of a single i.p. injection of ADR. Visinin like protein 1 (VLP1), peptidyl prolyl isomerase 1 (Pin1), and syntaxin 1 (SYNT1) showed differential levels in ADR treated mice relative to saline-treated controls. Triose phosphate isomerase (TPI), enolase, and peroxiredoxin 1 (PRX-1) showed significantly increased specific carbonylation in ADR treated mice brain. These results further support the notion ADR induces oxidative stress in brain despite not crossing the BBB, and that antioxidant intervention may prevent ADR-induced cognitive dysfunction.

Acrolein induces selective protein carbonylation in synaptosomes

Acrolein, the most reactive of the alpha,beta-unsaturated aldehydes, is endogenously produced by lipid peroxidation, and has been found increased in the brain of patients with Alzheimer's disease. Although it is known that acrolein increases total protein carbonylation and impairs the function of selected proteins, no study has addressed which proteins are selectively carbonylated by this aldehyde. In this study we investigated the effect of increasing concentrations of acrolein (0, 0.005, 0.05, 0.5, 5, 50 microM) on protein carbonylation in gerbil synaptosomes. In addition, we applied proteomics to identify synaptosomal proteins that were selectively carbonylated by 0.5 microM acrolein. Acrolein increased total protein carbonylation in a dose-dependent manner. Proteomic analysis (two-dimensional electrophoresis followed by mass spectrometry) revealed that tropomyosin-3-gamma isoform 2, tropomyosin-5, beta-actin, mitochondrial Tu translation elongation factor (EF-Tu(mt)) and voltage-dependent anion channel (VDAC) were significantly carbonylated by acrolein. Consistent with the proteomics studies that have identified specifically oxidized proteins in Alzheimer's disease (AD) brain, the proteins identified in this study are involved in a wide variety of cellular functions including energy metabolism, neurotransmission, protein synthesis, and cytoskeletal integrity. Our results suggest that acrolein may significantly contribute to oxidative damage in AD brain.

Purification and mass spectroscopic analysis of human CB1 cannabinoid receptor functionally expressed using the baculovirus system

The cannabinoid receptor 1 (CB1) cannabinoid receptor is an essential component of the cannabinergic system. It has been recognized as a therapeutic target for treating numerous diseases and is currently receiving considerable attention by the pharmaceutical community. Target-based drug design, utilizing three-dimensional information of receptor structure and ligand-binding motifs, requires significant amounts of purified protein. To facilitate the purification of CB1, we have expressed the receptor fused to various epitope tags using the baculovirus expression system. In addition, expression levels and ligand-binding profiles corresponding to the expressed fusion proteins have been compared. C-terminal histidine (His)-tagged CB1 gave a Bmax higher than most other systems previously reported in the literature, and was selected for subsequent metal affinity chromatography purification and mass spectroscopic (MS) analysis. Moreover, cells expressing C-terminal His-tagged CB1 were shown to inhibit forskolin-stimulated cyclic adenosine 3',5'-monophosphate (cAMP) production in a concentration-dependent manner in the presence of CP-55,940, confirming the expressed receptor's functional characteristics. A Western blot analysis of the purified receptor showed several forms of CB1, the most abundant being a 57 kDa monomeric protein. The purified CB1 preparations were subjected to protein digestion followed by MS. Fragments corresponding to >70% of the receptor were identified by this method, confirming the identity and purity of the expressed protein. The work presented here demonstrates that epitope-tagged CB1 can be expressed in sufficient amounts and purified to homogeneity for MS analysis. Moreover, these results will serve as a basis for future experiments aimed at characterizing the ligand-binding domains using covalently reacting receptor probes.

Covalent binding of acrylonitrile to specific rat liver glutathione S-transferases in vivo

Acrylonitrile (AN) is an industrial vinyl monomer that is acutely toxic. When administered to rats, AN covalently binds to tissue proteins in a dose-dependent but nonlinear manner [Benz, F. W., Nerland, D. E., Li, J., and Corbett, D. (1997) Fundam. Appl. Toxicol. 36, 149-156]. The nonlinearity in covalent binding stems from the fact that AN rapidly depletes liver glutathione after which the covalent binding to tissue proteins increases disproportionately. The identity of the tissue proteins to which AN covalently binds is unknown. The experiments described here were conducted to begin to answer this question. Male Sprague-Dawley rats were injected subcutaneously with 115 mg/kg (2.2 mmol/kg) [2,3-(14)C]AN. Two hours later, the livers were removed, homogenized, and fractionated into subcellular components, and the radioactively labeled proteins were separated on SDS-PAGE. One set of labeled proteins was found to be glutathione S-transferase (GST). Specific labeling of the mu over the alpha class was observed. Separation of the GST subunits by HPLC followed by scintillation counting showed that AN was selective for subunit rGSTM1. Mass spectral analysis of tryptic digests of the GST subunits indicated that the site of labeling was cysteine 86. The reason for the high reactivity of cysteine 86 in rGSTM1 was hypothesized to be due to its potential interaction with histidine 84, which is unique in this subunit.

Metabolism of DHEA by cytochromes P450 in rat and human liver microsomal fractions

Administration of dehydroepiandrosterone (DHEA) to rodents produces many unique biological responses, some of which may be due to metabolism of DHEA to more biologically active products. In the current study, DHEA metabolism was studied using human and rat liver microsomal fractions. In both species, DHEA was extensively metabolized to multiple products; formation of these products was potently inhibited in both species by miconazole, demonstrating a principal role for cytochrome P450. In the rat, use of P450 form-selective inhibitors suggested the participation of P4501A and 3A forms in DHEA metabolism. Human liver samples displayed interindividual differences in that one of five subjects metabolized DHEA to a much greater extent than the others. This difference correlated with the level of P4503A activity present in the human liver samples. For one subject, troleandomycin inhibited hepatic microsomal metabolism of DHEA by 78%, compared to 81% inhibition by miconazole, suggesting the importance of P4503A in these reactions. Form-selective inhibitors of P4502D6 and P4502E1 had a modest inhibitory effect, suggesting that these forms may also contribute to metabolism of DHEA in humans. Metabolites identified by LC-MS in both species included 16alpha-hydroxy-DHEA, 7alpha-hydroxy-DHEA, and 7-oxo-DHEA. While 16alpha-hydroxy-DHEA appeared to be the major metabolite produced in rat, the major metabolite produced in humans was a mono-hydroxylated DHEA species, whose position of hydroxylation is unknown.

Functional proteomic analysis of protein kinase C epsilon signaling complexes in the normal heart and during cardioprotection

Using two-dimensional electrophoresis, mass spectrometry, immunoblotting, and affinity pull-down assays, we found that myocardial protein kinase C epsilon (PKCepsilon) is physically associated with at least 36 known proteins that are organized into structural proteins, signaling molecules, and stress-responsive proteins. Furthermore, we found that the cardioprotection induced by activation of PKCepsilon is coupled with dynamic modulation and recruitment of PKCepsilon-associated proteins. The results suggest heretofore-unrecognized functions of PKCepsilon and provide an integrated framework for the understanding of PKCepsilon-dependent signaling architecture and cardioprotection.

Disulfide bonds of GM2 synthase homodimers. Antiparallel orientation of the catalytic domains

GM2 synthase is a homodimer in which the subunits are joined by lumenal domain disulfide bond(s). To define the disulfide bond pattern of this enzyme, we analyzed a soluble form by chemical fragmentation, enzymatic digestion, and mass spectrometry and a full-length form by site-directed mutagenesis. All Cys residues of the lumenal domain of GM2 synthase are disulfide bonded with Cys(429) and Cys(476) forming a disulfide-bonded pair while Cys(80) and Cys(82) are disulfide bonded in combination with Cys(412) and Cys(529). Partial reduction to produce monomers converted Cys(80) and Cys(82) to free thiols while the Cys(429) to Cys(476) disulfide remained intact. CNBr cleavage at amino acid 330 produced a monomer-sized band under nonreducing conditions which was converted upon reduction to a 40-kDa fragment and a 24-kDa myc-positive fragment. Double mutation of Cys(80) and Cys(82) to Ser produced monomers but not dimers. In summary these results demonstrate that Cys(429) and Cys(476) form an intrasubunit disulfide while the intersubunit disulfides formed by both Cys(80) and Cys(82) with Cys(412) and Cys(529) are responsible for formation of the homodimer. This disulfide bond arrangement results in an antiparallel orientation of the catalytic domains of the GM2 synthase homodimer.

Alkaline proteinase inhibitor of Pseudomonas aeruginosa. Interaction of native and N-terminally truncated inhibitor proteins with Pseudomonas metalloproteinases

The apr locus of Pseudomonas aeruginosa encodes alkaline proteinase (APR), a member of the metzincin metalloendopeptidase superfamily, and an 11.4-kDa alkaline proteinase inhibitor (APRin). We describe here the expression in Escherichia coli and characterization of full-length and N-terminally truncated APRin proteins. Fluorescence and circular dichroism spectra indicated that the recombinant proteins were folded into native-like structures. Analytical ultracentrifugation showed that APRin was monomeric and formed a 1:1 complex with APR. Binding of wild-type APRin to APR occurred with association (k(on)) and dissociation (k(off)) rate constants of 0.29 +/- 0.06 x 10(6) m(-1) s(-1) and 1.15 +/- 0.08 x 10(-6) s(-1) to give an equilibrium dissociation constant (K(D)) of approximately 4 x 10(-12) m (25 degrees C, pH 7.0, ionic strength 2.4 m). The association rate decreased by approximately 2-fold in 20% glycerol and increased by approximately 3-fold in 0.1 m NaCl. The glycerol effect suggests a diffusion-limited reaction, and the small salt effect indicates that electrostatic interactions contribute little to binding. Deletion of residues 1-10, 1-6, or 6-10 abolished inhibition, and deletion of residues 1-2, 1-3, 1-4, and 1-5 resulted in a progressively decreased affinity of APRin for APR (K(D) = 0.12 micrometer the Delta(1-5) mutant). Substitution of APRin residues 6-10 with a (Gly)(5) or (Pro)(5) linker restored inhibitory activity of the Delta(6-10) mutant but with a 100- and 50-fold reduction in K(D). Log k(on) for the full-length and truncated inhibitors correlated with the solvent-accessible surface area of their N-terminal regions, suggesting that increased interactions and/or desolvation of these residues in the transition state for binding contribute to the enhanced association rate. Treatment of APRin with pseudolysin, also secreted by P. aeruginosa, resulted in removal of residues 1-5. APRin was neither an inhibitor nor a substrate of other metzincins, including collagenase or gelatinases A or B.

Docosahexaenoic acid reverses cyclosporin A-induced changes in membrane structure and function

The use of a fish oil vehicle for cyclosporin A (CsA) can decrease the toxic effects of CsA but the mechanism is unclear. Here we examine the mechanism by which docosahexaenoic acid (DHA), a fish oil-derived polyunsaturated fatty acid, can alter the toxic effects of CsA on mouse organ function, endothelial macromolecular permeability, and membrane bilayer function. Mice given CsA and fish oil showed increased liver toxicity, kidney toxicity, incorporation of DHA, and evidence of oxidized fatty acids compared to control animals. We hypothesized that the toxic effects of CsA were primarily a result of membrane perturbation, which could be decreased if DHA were not oxidized. The presence of CsA (10 mol%) alone increased dipalmitoylphosphatidylcholine membrane permeability by seven fold over control (no CsA, no DHA). However, if non-oxidized DHA (15 mol%) and CsA were added to the membrane, the permeability returned to control levels. Interestingly, if the DHA was oxidized, the antagonistic effect of DHA on CsA was completely lost. While CsA alone increased endothelial permeability to albumin, the combination of non-oxidized DHA and CsA had no effect on endothelial macromolecular permeability. However the combination of oxidized DHA and CsA was no different than the effects of CsA only. CsA increased the fluorescence anisotropy of DPH in the liquid crystalline state of DPPC, while DHA decreased fluorescence anisotropy. However the combination of CsA and DHA was no different than DHA alone. We conclude that non-oxidized DHA can reverse the membrane perturbing effects of CsA, and the increases in endothelial macromolecular permeability, which may explain how fish oil is capable of decreasing the toxicity of CsA.

In vitro effects of zinc on markers of bone formation

Zinc deficiency is associated with a reduced rate of bone formation that can be corrected by supplementation of the deficient diet with adequate amounts of zinc. This study was conducted to examine the effects of zinc on bone cell parameters associated with bone formation. Tibiae were removed from 19-d-old chicken embryos and incubated for 48 h in Dulbecco's modified Eagle's medium supplemented with antibiotics, bovine serum albumin, and HEPES. The addition of zinc (25-200 g/dL) to tibial cultures resulted in a concentration-dependent increase in alkaline phosphatase activity, an increase in the incorporation of proline into bone protein and an increase in the post-translational oxidation of proline to peptidyl hydroxyproline. These effects of zinc were all diminished by the addition of 2,6-pyridine dicarboxylic acid, a chelator of zinc. The addition of either cycloheximide (10(-5)M), dactinomycin (10(-8)M), or hydroxyurea (10(-3)M) to tibial cultures also attenuated the effects of zinc. The effect of zinc on bone cell DNA synthesis was measured by following the incorporation of 3H-thymidine into DNA and by fluorometric measurement of cellular DNA content. These methods revealed that the addition of zinc to cultured tibiae resulted in a concentration-dependent increase in tibial DNA content and synthesis rate. The magnitude of the zinc-induced DNA increase was similar to the magnitude of the zinc-induced increases in alkaline phosphatase activity, proline incorporation, and hydroxyproline synthesis. Normalization of these latter responses to tibial DNA content yield data indicating that the effect of zinc on bone formation results from a zinc-induced increase in bone cell proliferation.

Cytoplasmic pH responses to carbonic anhydrase inhibitors in cultured rabbit nonpigmented ciliary epithelium

Carbonic anhydrase (CA) inhibitors lower the rate of aqueous humor (AH) secretion into the eye. Different CA isozymes might play different roles in the response. Here we have studied the effects of carbonic anhydrase inhibitors on cytoplasmic pH (pHi) regulation, using a dextran-bound CA inhibitor (DBI) to selectively inhibit membrane-associated CA in a cell line derived from rabbit NPE. pHi was measured using the fluorescent dye BCECF and the pHi responses to the cell permeable CA inhibitor acetazolamide (ACTZ) and DBI were compared. ACTZ markedly inhibited the rapid pHi changes elicited by bicarbonate/CO2 removal and readdition but DBI was ineffective in this respect, consistent with the inability of DBI to enter the cell and inhibit cytoplasmic CA isozymes. Added alone, ACTZ and DBI caused a similar reduction (0.2 pH units) of baseline pHi. We considered whether CA-IV might facilitate H+ extrusion via Na-H exchange. The Na-H exchanger inhibitor amiloride (1 mM) reduced pHi 0.52 +/- 0.10 pH units. In the presence of DBI, the magnitude of pHi reduction caused by amiloride was significantly (P < 0.05) reduced to 0.26 +/- 0.09 pH units. ACTZ similarly reduced the magnitude of the pHi reduction. DBI also reduced by approximately 40% the rate of pHi recovery in cells acidified by an ammonium chloride (20 mM) prepulse; a reduction in pHi recovery rate was also caused by ACTZ and amiloride. DBI failed to alter the pHi alkalinization response caused by elevating external potassium concentration, a response insensitive to amiloride but sensitive to ACTZ. These observations are consistent with a reduction in Na-H exchanger activity in the presence of DBI or ACTZ. We suggest that the CA-IV isozyme might catalyze rapid equilibration of H+ and HCO3- with CO2 in the unstirred layer outside the plasma membrane, preventing local accumulation of H+ which competes with sodium for the same external Na-H exchanger binding site. Inhibition of CA-IV could produce pHi changes that might alter the function of other ion transporters and channels in the NPE.

The influence of ascorbic acid on active sodium transport in cultured rabbit nonpigmented ciliary epithelium

PURPOSE

Cultured rabbit nonpigmented ciliary epithelium (NPE) transports ascorbic acid (ASC) inward through a sodium-dependent mechanism. This study was conducted to test whether Na-K transport is activated to export the additional sodium, which enters the cell in cotransport with ASC.

METHODS

Studies were conducted using a cell line derived from rabbit NPE. ASC uptake was measured using [14C]ascorbic acid. The ouabain-sensitive potassium (86Rb) uptake rate was measured as an index of active Na-K transport. Cellular sodium was measured by atomic absorption spectrophotometry or SBFI fluorescence.

RESULTS

In the presence of 200 microM ASC, ouabain-sensitive potassium (86Rb) uptake rate increased approximately 70%; lesser concentrations of ASC produced lesser increases. Phloridzin (100 microM) inhibited ASC uptake and inhibited the stimulatory effect of external ASC on 86Rb uptake. Dehydroascorbic acid (DHA) did not increase 86Rb uptake. Neither DHA nor ASC altered the Na,K-ATPase activity measured in isolated membrane material. External ASC appeared to stimulate active sodium transport through a mechanism involving an increase of cytoplasmic sodium. In the presence of 200 microM ASC, cellular sodium increased approximately 26%; studies with cells, sodium loaded by nigericin treatment, suggested that this sodium increase could account for the degree of 86Rb uptake stimulation observed in ASC-treated cells. However, the cellular sodium increase could not be explained simply on the basis of sodium entry through the ASC transporter. An additional sodium-entry pathway seemed to be activated in cells that accumulated ASC. Dimethylamiloride (DMA) abolished both the cellular sodium increase and the 86Rb uptake stimulation caused by ASC. DMA did not prevent ASC uptake.

CONCLUSIONS

ASC significantly stimulated active Na-K transport in cultured NPE. The mechanism appeared to involve activation of a DMA-sensitive sodium entry pathway, which caused cytoplasmic sodium concentration to increase.

In vitro bone resorption is dependent on physiological concentrations of zinc

The addition of physiological concentrations of zinc (25-200 (microg/dL) to Dulbecco's Modified Eagle's Medium containing tibiae from 19-d chick embryos resulted in a concentration-dependent increase in tibial content of tartrate-resistant acid phosphatase (TRAP) and an increase in bone resorption, as measured by tibial calcium release. This increase in bone resorption was additive to the resorptive effect resulting from the addition of 10(-9)-10(-7) M parathyroid hormone (PTH), but was not additive to similar effects produced by the addition of 10(-9)-10(-7) M prostaglandin E2 (PGE2). An inhibitor of prostaglandin synthesis, flurbiprofen (10[-6] M), did not influence the effect of zinc on bone resorption. However, the addition of 2,6-pyridinedicarboxylic acid (10[-3] M, 2,6-PDCA), a chelator of zinc, did attenuate the effects of zinc, as did the addition of an inhibitor of DNA replication (hydroxyurea, 10[-3] M). Hydroxyurea also attenuated the bone resorptive response to PGE2, but had no influence on the effects of PTH. These results indicate that physiological concentrations of zinc alter bone resorptive rates in vitro by a mechanism that is dependent on DNA replication.

Endogenous 7-oxocholesterol is an enzymatic product: characterization of 7 alpha-hydroxycholesterol dehydrogenase activity of hamster liver microsomes

Previously, we described a new metabolite derived from endogenous cholesterol in the presence of hamster liver microsomal protein and NADPH (Song et al., 1991, Biochem. Pharmacol. 41, 1439-1447). Through gas chromatography/mass spectral analysis of the metabolite and its methoxime-3-dimethyl-t-butylsilyl ether derivative, this metabolite has been definitively identified as 7-oxocholesterol. Isotope incorporation experiments using molecular 18O2 demonstrated that no oxygen atoms from molecular oxygen were incorporated into the product, 7-oxocholesterol, when 7 alpha-hydroxycholesterol was used as substrate. In contrast, one atom of 18O was incorporated into cholesterol from 18O2 during its metabolism to form 7 alpha-hydroxycholesterol. Formation of 7-oxocholesterol was dependent upon the presence of NADP+, 7 alpha-hydroxycholesterol, and hamster liver microsomes. This enzyme appears to be a membrane-bound protein and its activity was most abundant in liver microsomal fractions and to a lesser extent in mitochondrial fractions; little or no activity was observed in nuclei or cytosol. The enzyme activity was present in highest content in the livers of hamsters and was also observed in human and bovine liver microsomes, but not those of mouse, rabbit, or rat. The reaction was inhibited by 2'-AMP, but not by anti-NADPH:cytochrome-P450 oxidoreductase globulin, carbon monoxide, metyrapone, nor miconazole. In contrast to the previously characterized 3 beta-hydroxy-delta 5-C27-steroid oxidoreductase activity, NAD+ did not serve as an effective cofactor for 7-oxocholesterol formation. The ability of NADPH to partially serve as a cofactor in this reaction was shown to be due to a high NADPH-oxidase activity of hamster liver microsomes, thereby providing sufficient NADP+ to serve as the oxidizing pyridine nucleotide for the reaction. These results document the existence of a non-P450, NADP(+)-dependent 7 alpha-hydroxycholesterol dehydrogenase in liver microsomes which catalyzes this reaction. The product, 7-oxocholesterol, is produced enzymatically in the livers of hamsters and other mammals and may regulate bile acid metabolism or other processes due to its action as an oxysterol.

Quantitative analysis of 2-oxoglutarate in biological samples using liquid chromatography with electrochemical detection

This paper describes a technique for quantitative analysis of 2-oxoglutarate (alpha-ketoglutarate) in biological samples using liquid chromatography with electrochemical detection (LC-EC). This method utilizes a simplified, efficient sample preparation designed to select for 2-oxoglutarate and similar compounds by derivatization with phenylhydrazine. The response was linear over the range from 62.5 to 1000 ng/ml. The least quantifiable concentration was 62.5 ng/ml and the least detectable concentration was 25 ng/ml. To test the ability of the assay to measure 2-oxoglutarate in biological samples, this method was used to quantitate the 2-oxoglutarate content in chick osteoblast cultures and to determine the ability of the assay to accurately measure a standard addition of 500 ng/ml 2-oxoglutarate when added to a sample of the forementioned groups. The 2-oxoglutarate content of these cells was 6.67 +/- 1.20 ng/micrograms DNA or 105 +/- 18 ng/cell layer (mean +/- 95% confidence interval) and the assay accurately measured the standard addition. This method was also used to quantitate 2-oxoglutarate content in whole embryonic chick calvariae containing 6.40 +/- 0.95 ng/mg dry bone weight or 37.5 +/- 5.5 ng/bone. This assay provides significantly lower detection limits than the currently available procedures and is suitable for determination of 2-oxoglutarate in biological samples where very low amounts of 2-oxoglutarate are found. This method is the first application of LC-EC for quantitating 2-oxoglutarate.

Pharmacokinetics, acid-base balance and intraocular pressure effects of ethyloxaloylazolamide--a novel topically active carbonic anhydrase inhibitor

Studies evaluated a novel series of biscarbonylamides of 2-amino-1,3,4-thiadiazole-5-sulfonamide (2-ATS) for topical use as ocular hypotensive carbonic anhydrase inhibitors (CAI). Transcorneal accession rate constants (k(in)) for ethyloxaloylazolamide (EtOxAz), ethylsuccinylazolamide (EtSuxAz) and ethyladipoylazolamide (EtAdipAz), and activity against carbonic anhydrase (CA) were determined in vitro by an enzymatic assay and High Performance Liquid Chromatography (HPLC). The ocular hypotensive effect was measured by pneumatonometry on conscious normotensive New Zealand White (NZW) rabbits, using masked, randomly assigned paired-eye design for treatment vs. control. At various time points following treatment, aqueous humor, ciliary processes and corneal buttons were collected and assayed for drug concentrations using enzymatic assay and HPLC. Transcorneal accession rates for the novel compounds were 1.5 to 18 times that of the parent compound, acetazolamide (Actz). The activity factor for EtOxAz was 72.8 x 10(3) hr-1 of 23 times that of Actz. The activity factors for EtSuxAz and EtAdipAz were 6.8 and 1.1 x 10(3) hr-1, respectively. Subcutaneous administration of EtOxAz. EtSuxAz, and EtAdipAz, in 225 mumol kg-1 concentrations, induced a significant decrease in the intraocular pressure (IOP) at 1 hr post injection of 4, 5.8 and 6 mmHg for EtOxAz, EtSuxAz and EtAdipAz, respectively (P < 0.05 for each). Topical application of 75 mM EtOxAz lowered the IOP by 3.0 mmHg (P < 0.05). This effect was maximal after 60 min and persisted for at least 5 hr. EtSuxAz and EtAdipAz did not alter the IOP significantly when given topically. Subcutaneous administration of the three compounds was associated with acidosis (pH as low as 7.21). Topical application did not cause any changes in the acid-base balance. There was a direct correlation between the amount of drug delivered to the ciliary process and the magnitude of ocular hypotensive effect. Following topical application EtOxAz reached the ciliary epithelium in concentrations sufficient to inhibit more than 99.95% of the ciliary carbonic anhydrase (> 8 microM), while plasma drug concentrations were below the limit of detection by the assay (< 0.2 microM). Within the first hour after topical application, half of the EtOxAz was eliminated from the anterior uvea. In summary, EtOxAz is a topically effective CAI. Structural modifications of thiadiazole sulfonamides, with the increase of both water and lipid solubilities, improved the transcorneal accession while preserving sufficient CA inhibitory activity, resulting in a significant IOP decrease following topical application of EtOxAz.(ABSTRACT TRUNCATED AT 250 WORDS)

Topically active ocular carbonic anhydrase inhibitors: novel biscarbonylamidothiadiazole sulfonamides as ocular hypotensive agents

A novel homologous series of bis(carbonyl)amidothiadiazole sulfonamides has been synthesized for structure-activity relationship studies, and initial characterization has been performed. The goal was synthesis of thiadiazole derivatives with appropriate lipid and water solubilities for utility as topically (corneal application) active carbonic anhydrase (CA) inhibitors. This series has solubility properties and pKa which bracket those of acetazolamide--the prototypical CA inhibitor. All of these compounds are active as in vitro CA inhibitors, and are 10-25% as potent as acetazolamide as in vitro enzyme inhibitors. Two of these compounds act as ocular hypotensive agents after topical application of a single dose to the corneas of normotensive New Zealand albino rabbits. The efficacy of the lead compound of this series (in this one model) is approximately equivalent to that of topical CA inhibitors that are presently in clinical trial. None of these novel compounds reacts to an appreciable extent with free sulfhydryl groups (a predictor of toxicity). This family of compounds will be useful for future studies of ocular pharmacokinetics, as well as ocular and systemic effects of topical administration of CA inhibitors. These and future studies may lead to development of thiadiazole sulfonamides useful in the management of glaucoma.

Novel topical thiadiazoles and benzothiazoles as pharmacological probes of corneal endothelial function

Corneal transparency is maintained by an active transport system, located at the endothelial cell membranes. This bicarbonate-dependent pump counteracts the tendency of the corneal stroma to absorb water, swell and become opaque. Carbonic anhydrase inhibitors (CAI) are capable of attenuating the bicarbonate efflux, therefore causing thickening of the cornea. Eight novel sulfonamides were evaluated as potential probes for assessing the corneal endothelial functional reserves. Five of the six thiadiazoles and both benzothiazoles have demonstrated carbonic anhydrase inhibitory properties in vitro. Of the eight compounds tested, 2-ethyladipoyl-1,3,4-thiadiazole-5-sulfonamide (compounds III), 2-epoxy-1,3,4-thiadiazole-5-sulfonamide (compound V), and 2-acetamido-1,3,4-thiadiazole-5-N-methylsulfonamide (compound VI) have induced reversible corneal thickening. Although statistically significant (p < 0.05), the magnitude of the pachymetric effect did not exceed 6-10% of the total corneal thickness, probably because carbonic anhydrase (CA) is only one component of the active pump complex. The fact that a non-CAI (compound VI) was capable of inducing a reversible corneal thickening may suggest that other mechanisms are involved. Further studies will be conducted to identify a pharmacological agent capable of reversibly inhibiting the endothelial function in normal and diseased corneas, with a higher magnitude of effect.

Smokeless tobacco contains an inhibitor of prolyl hydroxylase activity

The effects of smokeless tobacco extract (STE) and various constituents of STE on prolyl hydroxylase activity were determined using enzyme extracted from chick embryos. STE inhibited prolyl hydroxylase activity in a concentration-dependent manner, but nicotine and anabasine had essentially no effect. Enzymatic activity was inhibited by zinc, but not by the other inorganic elements in STE; however, the zinc concentration in STE was not high enough to produce the observed inhibition. The inhibition by STE was diminished by increasing concentrations of 2-oxoglutarate, but not by increasing concentrations of other cofactors. Thus, STE contains an inhibitor of prolyl hydroxylase which may be competitive with 2-oxoglutarate.

Metabolism of arachidonic acid by isolated rabbit ciliary epithelium

We examined the ability of rabbit ciliary epithelium to metabolize arachidonic acid in vitro. The epithelium was homogenized and incubated with 14C-labeled arachidonic acid. 14C-labeled metabolites were extracted and then separated by thin layer chromatography. The range of arachidonic acid metabolites synthesized by ciliary epithelium was compared to the metabolites generated by rabbit iris-ciliary body. Ciliary epithelium produced substantial amounts of arachidonic acid metabolites that comigrated with 5-HETE and 12-HETE. Authenticity of the 12-HETE produced by ciliary epithelium was confirmed by gas chromatography/mass spectrometry. The ciliary epithelium generated only small amounts of the cyclooxygenase products, PGF2 alpha, PGE2, PGD2 and 6k-PGF1 alpha. In contrast, the iris-ciliary body produced large amounts of cyclooxygenase products such as PGF2 alpha and PGD2. The ability of the ciliary epithelium to generate 12-HETE is noteworthy since 12(R)-HETE is known to be capable of lowering intraocular pressure.

Inhibition of cell metabolism by a smokeless tobacco extract: tissue and species specificity

Smokeless tobacco contains a nonnicotine inhibitor of posttranslational modification of collagen (hydroxylation of [3H]proline) by cultured chick embryo tibias and osteoblasts. This study was undertaken to determine whether a methanol extract of smokeless tobacco (STE) containing the inhibitor has similar effects on collagen-producing cells and tissues other than bone. Its effects on DNA synthesis and cell proliferation (incorporation of [3H]thymidine) were also determined. Frontal bone, aorta, and cartilage were incubated for 2 days in medium containing STE. Glycolysis (lactate production) was stimulated by 80% in cartilage, but was not affected in the other tissues; medium alkaline phosphatase activity was unaffected. In frontal bone and cartilage, [3H] hydroxyproline content was decreased 88% and 57%, respectively, and [3H]proline content was decreased 68% and 37%, respectively; neither was affected in the aorta. Confluent cultures of collagen-producing mouse fibroblasts or primary osteoblasts obtained from chick embryo calvarias were incubated for 2 days in medium containing increasing concentrations of STE. Glycolysis and DNA synthesis were not affected. Cell proliferation was unaffected in fibroblasts, but was inhibited (34%) at the highest STE concentration in osteoblasts. AIPase activity was not detectable in fibroblast medium, but was decreased up to 72% in osteoblast medium. Inhibition of collagen synthesis by STE was concentration related in both cell types. At the highest concentration, [3H] hydroxyproline and [3H]proline contents in the cell layers were decreased to the following respective values: fibroblasts 56% and 45% and osteoblasts 50% and 29%, respectively. When incubation with STE was discontinued for 1 day, recovery did not occur. These findings suggest that inhibition of collagen synthesis by STE is not specific for bone, that collagen-producing cells are directly affected, and that recovery is not immediate. This inhibitor could contribute to the periodontal disease often seen in users of smokeless tobacco. Its identification and removal would produce a safer product.

Characteristics of cholesterol 7 alpha-hydroxylase and 7 alpha-hydroxycholesterol hydroxylase activities of rodent liver

A second cholesterol-derived metabolite in addition to 7 alpha-hydroxycholesterol was observed to be produced from endogenous microsomal cholesterol in the presence of hamster liver microsomal fractions and NADPH, when analyzed by HPLC using the method of Ogishima and Okuda (Anal Biochem 158: 228-232, 1986). However, only 7 alpha-hydroxycholesterol was produced in the presence of rat hepatic microsomal protein fractions and NADPH. The second metabolite was facilely produced when endogenous 7 alpha-hydroxycholesterol was incubated with hamster liver microsomes and NADPH, but not with rat liver microsomes. The second metabolite derived from either endogenous cholesterol or exogenous 7 alpha-hydroxycholesterol contained three hydroxyl groups as shown by mass spectrometric analysis. After oxidation of the 3 beta-ol group by cholesterol oxidase, the metabolite comigrated with 7 beta-hydroxycholest-3-one on normal phase HPLC, but was resolved from both 7 alpha- and 7 beta-hydroxycholest-3-one on reverse phase HPLC. The data indicate that the second metabolite is a hydroxylated product of 7 alpha-hydroxycholesterol, possibly cholest-5-ene-3 beta,7 alpha, 12 alpha-triol. Cholestyramine feeding increased production of both 7 alpha-hydroxycholesterol and its metabolite from endogenous cholesterol by 3-fold in hamster liver microsomes in vitro. However, the direct conversion of 7 alpha-hydroxycholesterol to the metabolite by hamster liver microsomes was not increased appreciably after cholestyramine feeding (20-30%). The hydroxylation of 7 alpha-hydroxycholesterol was similar in characteristics to cholesterol 7 alpha-hydroxylase activity in that it was dependent on NADPH, was inhibited by several known P450 inhibitors, and was affected by an inhibitory autobody elicited against rat hepatic NADPH: cytochrome P450 oxidoreductase. 5,6- and 7,8-Benzoflavone were poor inhibitors (IC50 approximately 1 mM) of cholesterol 7 alpha-hydroxylase activity in liver microsomes from cholestyramine-fed rats, but caused a striking enhancement of the 7 alpha-hydroxylase activity of liver microsomes from untreated rats in vitro. In contrast, 7,8-benzoflavone inhibited cholesterol 7 alpha-hydroxylase and 7 alpha-hydroxycholesterol hydroxylase activities of microsomes from normal and cholestyramine-fed hamsters. However, 5,6-benzoflavone stimulated cholesterol 7 alpha-hydroxylase activity in liver microsomes from normal and cholestyramine-fed hamsters, but inhibited 7 alpha-hydroxycholesterol hydroxylase activity by approximately 50%. These results suggest that hepatic cholesterol 7 alpha-hydroxylase and 7 alpha-hydroxycholesterol hydroxylase activities apparently involve multiple forms of cytochrome P450 in untreated and cholestyramine-treated hamsters.

Inhibition of hepatic microsomal cytochrome P-450 dependent monooxygenation activity by the antioxidant 3-tert-butyl-4-hydroxyanisole

The efficacy of 3-tert-butyl-4-hydroxyanisole (BHA) as a chemopreventive agent against chemically induced cancer or toxicity may involve the direct modulation of cytochrome P-450 dependent monooxygenase function. This hypothesis was investigated by using purified rabbit cytochrome P-450IA2 and P-450IIB4 in a reconstitution system with purified NADPH:cytochrome P-450 oxidoreductase and L-alpha-dilauroylphosphatidylcholine. BHA caused a concentration-dependent decrease in cytochrome P-450IIB4 dependent 7-ethoxycoumarin O-deethylation, cyclohexane hydroxylation, and benzphetamine N-demethylation activities (IC50; 28, 75, and 290 microM, respectively) and in cytochrome P-450IA2 dependent 7-ethoxyresorufin O-deethylation and acetanilide para hydroxylation activities (IC50 approximately 225 microM). The inhibition of monooxygenation activity was accompanied by redox cycling due to the tert-butylquinone produced during BHA metabolism, as measured by increased NADPH and oxygen consumption or hydrogen peroxide and superoxide anion production. Glutathione was shown to reverse this redox cycling phenomenon but did not reverse the BHA-dependent inhibition of monooxygenation activity. Using standard steady-state kinetic analyses, BHA was shown to be a mixed-type competitive inhibitor of benzphetamine metabolism by cytochrome P-450IIB4, suggesting that BHA does not simply compete as an alternate substrate for the hemoprotein but must also bind to another catalytically functional form of cytochrome P-450. BHA was shown to bind as a ligand to both purified and microsomal cytochrome P-450IA2, resulting in a low to high (type I) spin-state perturbation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of chronic carbonic anhydrase inhibitor therapy on bone mineral density in white women

A limited, dual-photon absorptiometry, single-center study of bone mineral density (BMD) was conducted on white female glaucoma subjects who were chronic users of the carbonic anhydrase (CA) inhibitors acetazolamide (Az) or methazolamide (Mz). In postmenopausal subjects long-term (greater than 4 years) CA inhibitor use was associated with a bone-sparing effect as judged by spinal BMD in comparison to controls matched for age, sex, weight, and ethnic group or in comparison to a national normative data base. Short-term (0-2 years) postmenopausal CA inhibitor users and premenopausal subjects using CA inhibitors showed no sparing of spinal BMD. Femoral neck BMD was not affected by CA inhibitor therapy in any of the groups. This study supports a proposed role for carbonic anhydrase in human bone resorption and suggests a possible future utility for carbonic anhydrase inhibitors in prophylaxis or management of primary involutional osteoporosis. Future studies are necessary to verify and expand these findings, assess the effects of CA inhibitors on bone mechanical competence, and further develop CA inhibitors with some specificity for bone.

Cardiac output and the blood pressure increase in deoxycorticosterone acetate-salt hypertension after nicotine infusion

We wished to determine if nicotine exaggerates the blood pressure increase in deoxycorticosterone (DOCA)-salt hypertension. Uninephrectomized, male Sprague-Dawley rats were implanted with DOCA pellets (75 mg) and placed on a 5.2% salt diet for sixteen days and then infused with nicotine (DOCA-Nicotine; 2.4 mg/kg/day) or vehicle (DOCA-Sham). Control animals were treated with vehicle (Control) or nicotine (Control-Nicotine). The DOCA-Nicotine group had significantly greater tail-cuff blood pressures than the DOCA-Sham group by one week of nicotine infusion. At 2.5 weeks of nicotine infusion the DOCA-Nicotine rats had significantly greater tail-cuff blood pressures, direct arterial blood pressures, and cardiac outputs compared to the DOCA-Sham animals. Renal blood flows were similar in the two groups. Control-Nicotine animals demonstrated no response to nicotine during 2.5 weeks of infusion. We conclude that in the DOCA-salt rat nicotine induces an exaggerated rise in blood pressure and that the mechanism involves an increase in cardiac output.

Ethyl carbamate metabolism: in vivo inhibitors and in vitro enzymatic systems

The metabolism of ethyl carbamate and the localization of its metabolites have been shown to be almost completely inhibited by ethanol in the mouse [Waddell, Marlowe, Pierce: Food Chem. Toxicol.25, 527 (1987); Yamamoto, Pierce, Hurst, Chen, Waddell: Drug Metab. Dispos. 16, 355 (1988)]. The enzyme system catalyzing this metabolism which is inhibited by ethanol now has been further investigated in both in vivo and in vitro studies. There is a direct, highly significant relationship between the extent of metabolism of ethyl carbamate and covalent binding of metabolites to liver protein. Paraoxon, carbaryl, CCl4 ethanol, methimazole, 4-methylpyrazole, diethyl maleate, ethyl N-hydroxycarbamate, and t-butyl carbamate inhibit, to different extents, the metabolism of ethyl carbamate in vivo; SKF-525A, CoCl2, Cacyanamide, chloral hydrate, 2-oxo-4-thiazolidine carboxylic acid, allopurinol, and methyl carbamate do not. Porcine liver esterase, yeast aldehyde dehydrogenase and mouse liver catalase catalyzed the metabolism in vitro; dog or bovine catalase, acid phosphatase, alcohol dehydrogenase, or carbonic anhydrase did not under the conditions tested. Paraoxon, 4-methylpyrazole, carbaryl, and NaF significantly inhibited the hydrolytic activity of mouse liver homogenates toward p-nitrophenyl acetate; ethanol or ethyl carbamate did not. However, each of these, except 4-methylpyrazole, inhibited the metabolism of ethyl carbamate by mouse liver homogenate or porcine liver esterase to about the same extent. Ion exchange chromatography of mouse liver cytosol revealed that the fraction with ability to metabolize ethyl carbamate co-chromatographed almost exactly with the ability to hydrolyze p-nitrophenyl acetate. It is proposed that ethyl carbamate is metabolized in the mouse, at least partially, by esterases; however, metabolism by other enzyme systems cannot be excluded.

Enhanced decomposition of oxyferrous cytochrome P450CIA1 (P450cam) by the chemopreventive agent 3-t-butyl-4-hydroxyanisole

The efficacy of 2(3)-t-butyl-4-hydroxyanisole (BHA) and other chemicals as chemopreventive agents against chemically induced cancer or toxicity may involve direct modulation of cytochrome P450 activity. Direct interaction of BHA with cytochrome P450 was investigated using substrate-bound, oxyferrous cytochrome P450CIA1 either in a reconstituted system containing cytochrome P450CIA1, putidaredoxin, and putidaredoxin reductase with NADH as electron donor or in the absence of physiological electron donors. In the reconstituted system, BHA caused a concentration-dependent decrease in the production of 5-exo-hydroxycamphor and a substoichiometric increase in hydrogen peroxide production. However, BHA did not appreciably inhibit either NADH oxidation or oxygen utilization under conditions optimal for accumulation of oxyferrous cytochrome P450CIA1 during steady-state metabolism of camphor. In the absence of electron donor, BHA enhanced decomposition of the ternary oxyferrous substrate complex of cytochrome P450CIA1 without the formation of any apparent spectral intermediate(s). The rate of decomposition of the oxyferrous complex was pseudo-first order and was dependent upon the concentration of BHA present. Enhanced decomposition of the complex was not attributable to catalytic turnover of cytochrome P450CIA1 (i.e., acquisition of a second electron from an indeterminate source) since no appreciable metabolism of either camphor or BHA was observed. The enhanced decomposition was accompanied by a substoichiometric increase in hydrogen peroxide production, suggesting that BHA may facilitate four-electron reduction of molecular oxygen to water. These results indicate that BHA inhibits cytochrome P450 function, presumably by enhancing autoxidation of the substrate-bound oxyferrous complex.

Acute acrylonitrile toxicity: studies on the mechanism of the antidotal effect of D- and L-cysteine and their N-acetyl derivatives in the rat

Thiol-containing antidotes for acute acrylonitrile (AN) toxicity may exert their action by chemically reacting with AN, by replacing critical sulfhydryl groups cyanoethylated by AN, and by detoxifying cyanide produced from AN metabolism. We have evaluated the ability of the optical isomers of cysteine and N-acetylcysteine to act as antidotes against AN toxicity in order to assess the relative importance of each of these three antidotal mechanisms. The toxicity of AN was determined in male Sprague-Dawley rats and compared to the toxicity determined after treatment with 2 mmol/kg of thiol antidote by computing a protective index (median lethal dose with antidote/median lethal dose without antidote). The protective indices of L-cysteine, D-cysteine, N-acetyl-L-cysteine, and N-acetyl-D-cysteine were 2.03, 1.97, 1.76, and 1.25, respectively. Measurements of urinary mercapturates, derived from the non-oxidative pathway of AN metabolism, indicated that none of the antidotes was able to significantly increase the excretion of these metabolites. Blood cyanide generated from the oxidative metabolism of AN and butyronitrile was also determined. All of the antidotes, except N-acetyl-D-cysteine, lowered blood cyanide levels. A comparison of these results with the predicted relative abilities of the enantiomers to participate in each of the three antidotal mechanisms leads to the conclusion that, under these experimental conditions, the best correlation exists with the cyanide detoxification mechanism.

Effects of ebselen on arachidonate metabolism by ocular and non-ocular tissues

The formation of cyclooxygenase products in rabbit and rat ocular and non-ocular tissues in vitro, detected by radio-thin-layer chromatography, was inhibited in a concentration-dependent manner by ebselen (PZ 51), an anti-inflammatory seleno-organic compound which has glutathione peroxidase and anti-oxidant activities. The exception was prostaglandin F2 alpha (PGF2 alpha) formation in the rabbit irisciliary body which was stimulated by ebselen in the concentration range 2-10 microM. These observations were confirmed by gas chromatography-mass spectrometry. The concentration that inhibited 50% of prostaglandin biosynthesis (IC50) in the rabbit iris-ciliary body was 9.3 microM. Ebselen also inhibited the formation of 12-hydroxyeicosatetraenoic acid (12-HETE) in rabbit and rat ocular tissues and rabbit platelets. The IC50 in the rabbit cornea was 4 microM, whereas higher concentrations were generally required to achieve similar inhibition in other tissues. The formation of 12-HETE by rabbit spleen, however, was not decreased by ebselen at concentrations that were inhibitory in other tissues.

Effects of subchronic nicotine administration on central dopaminergic mechanisms in the rat

Nicotine was administered acutely and subchronically (14 days) to determine whether various synaptic mechanisms are selectively altered in the nigrostriatal and mesolimbic dopaminergic systems in the rat. When added to tissue preparations in vitro, nicotine had no effects on tyrosine hydroxylase, synaptosomal uptake of [3H]dopamine or binding of [3H]spiperone to D2 receptors in either system. However, acute treatment in vivo stimulated tyrosine hydroxylase activity in the nucleus accumbens. This effect was prevented by pretreatment with a nicotinic antagonist, suggesting that it was mediated by nicotinic receptors. Since subchronic exposure to nicotine had no effect on tyrosine hydroxylase, it appears that tolerance develops to this action. In vivo treatment with nicotine did not alter dopamine uptake or receptor binding. The results suggest that, in doses which result in moderate plasma levels, nicotine has selective stimulant actions on nerve terminals of the mesolimbic system.

Qualitative and quantitative analyses of phenol, phenylglucuronide, and phenylsulfate in urine and plasma by gas chromatography/mass spectrometry

Phenol and related compounds are toxic agents to which humans are exposed. Analysis of phenolic compounds may be used as an index of exposure. In this report a method for analysis of phenol, phenylglucuronide, phenylsulfate, and related mono- and dihydroxybenzenes as their propanoate esters by gas chromatography/mass spectrometry is presented. The use of this derivatization technique increases the sensitivity of the analysis by improving chromatographic performance and introducing a traceable "reporter" group into the analyte. This method has also been adapted, by using selected ion monitoring (SIM), to the quantitative analysis of phenol.

Determination of ethyl carbamate in distilled alcoholic beverages by gas chromatography with flame ionization or mass spectrometric detection

Quantitative methods are detailed for determination of ethyl carbamate in distilled alcoholic beverages by capillary gas chromatography with flame ionization detection (GC/FID) and by packed-column gas chromatography/mass spectrometry (GC/MS) using selected ion monitoring. Five g samples of distillate of known ethanol concentration are diluted with water to 25% ethanol (v/v), washed with petroleum ether, and extracted with dichloromethane prior to GC/FID or GC/MS analysis. As necessary, sample extracts that exhibit GC/FID interference are passed through alumina for additional cleanup. When internal standards (tert-butyl carbamate and n-butyl carbamate for GC/FID, or ethyl 13C-15N-carbamate for GC/MS) were used for quantitation, the limit of detection for ethyl carbamate was in the range of 5-25 ppb. Coefficients of variation ranged from 3.5 to 6.0% for GC/FID determinations, and from 1.4 to 3.2% for GC/MS. Correlation between methods for 22 random distillate samples ranging in concentration from approximately 40 to 800 ppb gave a correlation coefficient (r) of 0.996.

Inhibition of the metabolism of urethane by ethanol

Ethanol has been shown to inhibit the localization of [ethyl-1-14C] urethane in the male mouse, but the effect of ethanol on the metabolism of urethane has not been clarified. Consequently, the concentration of unchanged urethane was determined in the blood of male mice up to 11 hr after oral administration of urethane with or without ethanol. A high and constant blood level of urethane persisted for 8 hr after the administration of an ethanolic solution of [ethyl-1-14C] urethane (125 mumol/kg, 10 muCi/20 g of mouse, 5 g of ethanol per kg, po); the blood level of ethanol was at or above 150 mg/dl during these 8 hr. In contrast, rapid clearance of radioactivity was observed in mice treated with [ethyl-1-14C]urethane dissolved in water. Coadministration of ethanol with urethane decreased the rate of 14CO2 expiration; furthermore, covalent binding with liver protein was delayed about 8 hr and was less than that in the group treated with urethane in water. The metabolism of urethane and production of 14CO2 from [carbonyl-14C]urethane by mouse liver homogenate in vitro were inhibited by the presence of ethanol (greater than 10 mM); these concentrations of ethanol in vitro are about the same as those that are inhibitory in vivo, but the extent of inhibition suggests that the liver is not the only site of metabolism of urethane. These results indicate that ethanol can inhibit the initial metabolism of urethane, prevent the formation of active metabolites, and allow urethane to persist in blood.

Bone-targeted carbonic anhydrase inhibitors: effect of a proinhibitor on bone resorption in vitro

Many investigations have indicated a functional role for carbonic anhydrase in the mediation of hormone-stimulated bone resorption. These studies depend heavily on the use of heterocyclic sulfonamide inhibitors of carbonic anhydrase. These drugs have effects on many tissues other than bone, and some of these effects confound the interpretation of studies of the role of carbonic acid in bone metabolism. A novel, "bone-targeted" sulfonamide has been produced to obviate these extraosseous effects. This compound (designated WP-1) is the combination of tetracycline and acetazolamide, such that the acetazolamide is not an active inhibitor. Hydrolysis of WP-1 yields an active carbonic anhydrase inhibitor. WP-1 has a marked affinity for bone mineral, allowing deposition of the drug in bone. At a concentration of 10(-5) M, WP-1 attenuates parathyroid hormone stimulated net release of calcium from neonatal rat calvaria in culture. WP-1 is the first member of a class of drugs which may prove useful as pharmacological probes in the study of bone metabolism.

Inhibition of thermolysin by bifunctional N-carboxyalkyl dipeptides

A series of N-carboxyalkyl derivatives of L-leucyl-L-alanine was synthesized and tested as inhibitors of the zinc endoproteinase thermolysin. The purpose of the study was to determine whether bifunctional N-carboxyalkyl compounds with secondary metal coordinating groups are more potent inhibitors than analogs lacking such an additional binding function. Reductive condensation of L-leucyl-L-alanine (LA) with pyruvic, oxalacetic, alpha-ketoglutaric, 2-oxopentanoic, 4-ethyloxalacetic, or imidazoylpyruvic acids gave N-[1(R, S)-carboxyethyl]-LA (I), N-[1(R, S)-carboxy-2-carboxyethyl]-LA (II), N-[1(R, S)-carboxy-3-carboxypropyl]-LA (III), N-[1(R, S)-carboxy-n-butyl]-LA (IV), N-[1(R, S)-2-ethylcarboxyethyl]-LA (V), and N-[1(R, S)-carboxy-2-(4-imidazoyl-ethyl]-LA (VI), respectively. Values of KI determined with furylacryloyl-Gly-Leu-NH2 as substrate were 116 +/- 21, 7.4 +/- 1.8, 6.3 +/- 0.5, 19.7 +/- 1.5, 17.0 +/- 1.0, and 3.3 +/- 0.1 microM for compounds I-VI, respectively. Although bifunctional inhibitors II, III, and VI were indeed more potent than I, they were not much more effective than analogs IV and V that contained noncoordinating functionalities of comparable size. The results do not provide strong evidence for chelation of the active site zinc ion as proposed, although such interactions do not appear to be ruled out altogether.

Inhibition of the localization of urethane in mouse tissues by ethanol

[ethyl-1-14C]Urethane in water or in 12% ethanol was administered orally to male A/JAX mice and 1 hr later the mice were frozen and processed for whole-body autoradiography to identify sites of localization of radioactivity. When the [14C]urethane was administered in water, radioactivity was localized in the liver and bile, the salivary, seromucous and Harderian glands, the bone marrow and pancreas and the stomach and intestinal epithelia. When the labelled urethane was administered in 12% ethanol, localization of radioactivity in each of these sites was almost completely inhibited; radioactivity was still seen within the lumen of the stomach and intestine. Using a defined chemical system, no transesterification was observed between urethane and 12% aqueous [2H6]ethanol at pH 1.5 in 80 min. The inhibition of the localization of radioactivity in the tissues appears to be due most probably to blocking of the metabolism of urethane in tissues. This suggests that ethanol may inhibit the carcinogenicity of urethane in mice.

Effects of heterocyclic sulfonamides on bone metabolism

Sulfonamide inhibitors of carbonic anhydrase attenuate parathyroid hormone and vitamin D3 induced bone resorption. Parathyroid hormone stimulates bone cell accumulation of cAMP in the presence of concentrations (10(-7) - 10(-3) M) of acetazolamide (an inhibitor of carbonic anhydrase) that are antagonistic to bone resorption. Bone cell acid phosphatase activity and lactic acid production are stimulated by parathyroid hormone or vitamin D3. These cellular responses are not influenced by the presence of acetazolamide (10(-4) M). Bone cells incubated in the presence of parathyroid hormone reveal an increase in carbonic anhydrase like activity. This activity is lost upon heating a supernatant of the bone cell population or upon treatment of the supernatant with appropriate concentrations of acetazolamide.

Procedures for measuring cytochrome P-450-dependent hydroxylation activity in reproductive tissues

Cytochrome P-450 is present in the endoplasmic reticulum at varying concentrations in almost all tissues. However, the existence and role of cytochrome P-450 in normal and neoplastic reproductive tissues has not been clearly demonstrated. Our interest lies in the possibility that variations in cytochrome P-450 levels may influence the responsiveness of breast and endometrial carcinomas to endocrine therapy. This may be of particular importance with agents such as tamoxifen where hydroxylation reactions are known to alter therapeutic activities. Therefore, a simple, sensitive spectrophotometric assay for determining levels of cytochrome P-450-dependent cyclohexane hydroxylase activity in breast and uterine microsomes has been developed. Cyclohexane was chosen as a substrate because of the relatively high levels of cyclohexane hydroxylase activity in tumor microsomes and because cyclohexane serves as a substrate for several forms of cytochrome P-450. In order to confirm the results of the spectrophotometric assay, a direct method utilizing isotope dilution gas chromatography/mass spectrometry (GC/MS) has been developed for detecting low levels of the hydroxylated product, cyclohexanol. By employing a stable isotopically labeled analog of cyclohexanol (cyclohexanol-d12), good agreement was demonstrated between the simple, indirect method (measuring NADPH oxidation at 340 nm) and the more complex, direct method (measuring cyclohexanol formation) utilizing GC/MS. The agreement of results obtained using these two techniques indicates that they are equally valid measures of NADPH-dependent cyclohexane hydroxylase activity. The use of the spectrophotometric method is proposed for rapid, multiple assays such as in the clinical setting, reserving GC/MS analysis for use as a research tool.

Effect of sulfonamides on the hypercalcemic response to vitamin D

Parathyroidectomized rats were fasted for twenty-four hours then treated with 10(6) units/kg of vitamin D3. Twelve hours later the animals were bilaterally nephrectomized and treated with either the appropriate control solution or one of the following: acetazolamide, methazolamide, ethoxzolamide or CL 13,850. Animals treated with the vitamin exhibited an increase in plasma calcium of approximately 5 mg/dl. This response was antagonized by treatment with acetazolamide, methazolamide or ethoxzolamide. These agents are all sulfonamide inhibitors of carbonic anhydrase. CL 13,850, a structural analog of acetazolamide that is devoid of enzyme inhibitory activity, was also devoid of inhibitory activity with respect to the hypercalcemic response to vitamin D3. Acetazolamide inhibited the response to the vitamin at doses yielding ultrafiltrable plasma drug concentrations of approximately 10(-5) to 10(-4) M. The hypercalcemic response observed following the administration of the active metabolite of vitamin D3 (1,25-dihydroxyvitamin D3) was attenuated by treatment with acetazolamide.

Sulfonamide inhibition of bone resorption: lack of a hypophosphatemia

Calcitonin and acetazolamide inhibit bone resorption in the ureter-ligated rat. Calcitonin treatment results in an ensuing hypocalcemia and hypophosphatemia. Although acetazolamide treatment results in a hypocalcemic response similar to that seen with calcitonin, plasma phosphate concentrations increase or remain unchanged after drug treatment. Data are presented indicating that acetazolamide exhibits two effects that influence blood phosphate. Drug treatment of ureter-ligated rats results in an inhibition of bone resorption which tends to lower blood phosphate concentrations. However, this effect is masked by a drug-induced hypercapnia which results in an increase in plasma phosphate concentrations. Elevation of blood pCO2 also attenuates the hypophosphatemic response to calcitonin.